Open heart surgery has been practiced for a number of years and techniques for protection of the patient have been under study for all of this period. When the blood of the patient is by-passed to an extracorporeal support system which maintains the pumping function of the heart and the oxygenation function of the lungs, it is important that the heart itself be protected from damage. In the circumstances of heart surgery, the possibility of damage to the heart is greatly reduced by cooling and administering drugs to the heart in a technique called "clear" or "crystalloid" cardioplegia. Another method of cardioplegia is "blood" cardioplegia wherein the actual blood of the patient is used to cool the heart and as the vehicle for delivery of the cardioplegic solution.
Various methods for achieving cardioplegia have been used. Literature on the subject includes:
A Simple Method of Cold Coronary Perfusion, Hillel Lakes, M.D. et al. The Annals of Thoracic Surgery, Vol. 25, No. 4, April 1978 PA1 Cold Cardioplegia Versus Hypothermia for Myocardial Protection, The Journal of Thoracic and Cardiovascular Surgery, Vol. 76, No. 5, November 1978 PA1 (a) a primary chamber having an entrance way for liquid disposed at the bottom, said primary chamber capable of providing a passageway for liquid leaving said entrance way, and said primary chamber having a greater cross-sectional area than said entrance way, such that when liquid enters said primary chamber from said entrance way the average velocity of the liquid is caused to decelerate; and PA1 (b) a secondary chamber separated from said primary chamber by a dam, the area above said dam providing a passageway for liquid flowing from said primary chamber to said secondary chamber, said secondary chamber having a shelf extending into said secondary chamber in a direction towards said dam, but not extending so far into said secondary chamber as to block the passage of liquids through said secondary chamber, and said secondary chamber having an outlet for liquid disposed at the bottom of said secondary chamber. PA1 (a) a primary chamber having an entrance way for infusion fluid disposed at the bottom, said entrance way adapted for connection with said infusion fluid inlet, said primary chamber capable of providing a passageway for infusion fluid leaving said entrance way, and said primary chamber having a greater cross-sectional area than said entrance way, such that when infusion fluid enters said primary chamber from said entrance way the average velocity of said infusion fluid is caused to decelerate; and PA1 (b) a secondary chamber separated from said primary chamber by a dam, the area above said dam providing a passageway for infusion fluid flowing from said primary chamber to said secondary chamber, said secondary chamber having a shelf extending into said secondary chamber in a direction towards said dam, but not extending so far into said secondary chamber as to block the passage of infusion fluid through said secondary chamber, and said secondary chamber having said outlet for infusion fluid disposed at the bottom of said secondary chamber.
Additionally, cardioplegia delivery systems have been disclosed in commonly assigned U.S. patents, U.S. Pat. No. 4,433,971; U.S. Pat. No. 4,427,009; and U.S. Pat. No. 4,416,280. In all of these systems the cardioplegia fluid is pumped through a tube set, cooled, debubbled, and the pressure and temperature of the fluid are measured before it is delivered to the patient through a cannula.